Polyethylene terephthalate (PET) is a thermoplastic polymer extensively used for packaging applications due to its features such as acceptable process ability and barrier properties, recyclability and compatibility with food applications. Further, the packaging articles prepared from PET are light in weight, unbreakable and have aesthetic appeal.
Packaging articles prepared from PET and used for packaging foodstuffs such as fruit juices, food concentrates, sport drinks, ketchups, sauces and jams need to be hot finable to achieve desired shelf-life of the products.
Extensive research is being carried out to improve hot fillability of polyethylene terephthalate by adding isosorbide monomer. The polyethylene terephthalate modified by isosorbide exhibits glass transition temperature (Tg) from 82 to 180° C. based on the quantity of isosorbide used in the polyethylene terephthalate.
For instance, U.S. Pat. No. 6,818,730 suggests a process for producing isosorbide-containing polyesters.
US20120177854 suggests a process for the preparation of polyester by using terephthalic acid, cyclohexanedimethanol and isosorbide.
U.S. Pat. No. 5,959,066 suggests a method for the preparation of polyester. In the method, a terephthaloyl moiety; optionally, one or more other monomers containing an aromatic diacid moiety; a monomer comprising an ethylene glycol moiety; a monomer comprising an isosorbide moiety; optionally, one or more other monomers comprising a diol moiety; and optionally, a monomer comprising a diethylene glycol moiety, are combined with a condensation catalyst and heated to prepare the polyester.
U.S. Pat. No. 6,025,061 suggests a method for making a sheet. The method consists of preparing a polyester and producing a sheet from the polyester. The polyester contains terephthaloyl moieties; optionally, one or more other aromatic diacid moieties; ethylene glycol moieties; isosorbide moieties; and, optionally, one or more other diol moieties, wherein said polyester has an inherent viscosity of at least about 0.35 dL/g.
U.S. Pat. No. 6,063,464 suggests a process for producing polyesters. The process contains steps of combining one or more monomers comprising a diacid moiety; a monomer comprising an isosorbide moiety; and one or more monomers comprising another diol moiety; with a condensation catalyst and heating to a polymerization temperature to produce a polyester polymer having the diacid moieties, the isosorbide moieties and other diol moieties. The polyester obtain by the process suggested in U.S. Pat. No. 6,063,464 has an inherent viscosity of at least about 0.15 dL/g.
The polyester containers obtained by using polyester obtained by these suggested processes suffer from several drawbacks due to the hygroscopic nature and high reactivity of isosorbide. Isosorbide present in the container reacts easily with atmospheric moisture and readily undergoes oxidative degradation and discoloration. Due to these properties of isosorbide, the polyester containers are not transparent and do not provide requisite barrier properties and therefore cannot be used in several applications in food industry.
Further, the polyester containers may not be used for preparing hot fill packaging containers as they cannot withstand a temperature of 90° C. and tend to undergo deformation and shrinkage.
Therefore, in light of the foregoing drawbacks, there is a felt need for polyester that is capable of withstanding high temperature without undergoing any deformation and shrinkage along with acceptable physical and chemical properties for packaging applications. Further, there is a need for a process for preparing polyester that is capable of withstanding high temperature without undergoing any deformation and shrinkage.